An actuator is a device that converts input energy into mechanical energy. Various types of actuators are available for a variety of applications. For example, piezoelectric actuators (referred to herein as piezo actuators) achieve displacement by directly applying an electrical signal to a solid material (typically a crystal or ceramic material). Piezo actuators feature relatively high displacement accuracy, large force generation and high response times. Applications for the use of piezo actuators include, for example, industrial equipment requiring precision position control such as ultrafine-movement stage of semiconductor exposure systems, precision positioning strobes for scanning tunnel microscopy, printers, etc.
A piezo actuator may be driven by an amplifier such as a voltage mode amplifier or a transconductance amplifier. A transconductance amplifier generally provides better linearity performance than a voltage mode driver. The velocity of the movement of the piezo actuator is proportional to the current through the actuator. If it is desired for the piezo actuator to stop moving, the current should be set to zero current (i.e., turned off). However, a sudden change in current with respect to time (i.e., high di/dt) can damage the piezo actuator. There are other reasons for turning off current to a piezo actuator. For example, a user may want to sense the piezo actuator's parameters such as voltage, position, leakage current, etc. During such sensing, the current to the actuator should be ceased. However, as noted above, a sudden change in piezo actuator current can be harmful to the device.